A large frame heavy duty industrial gas turbine (IGT) engine is typically used to drive an electric generator and produce electrical energy. These engines can produce over 200 MW of electric power. For example, a large frame industrial gas turbine engine may output almost 300 MW of electrical power. An IGT engine will have a compressor with multiple rows or stages of rotor blades and stator vanes, a combustor with multiple can combustors arranged in an annular array (also referred to as a can annular combustor), and a turbine with multiple rows of rotor blades and stator vanes. An aero engine typically has an annular combustor instead of multiple can combustors arranged in an annular array as in the IGT engines.
The largest hurdle to introducing new technologies into large frame power generation gas turbine engines is the risk that the new technology may fail during operation of the engine and result in tens of millions of dollars in equipment damage and possibly the cost of replacement electricity during the down time of the power plant. Because an owner of one of these engines is very reluctant to allow for the use of the engine in testing a new technology and, as a result, it is very difficult to introduce new technologies into a utility power generation plant, most power generation manufacturers have test facilities to test as much as possible the components prior to going into production. Unfortunately, the cost of test facilities and running the tests prohibits extensive testing and usually only allows for infant mortality issues to be discovered prior to installation of a new gas turbine engine at the utility site.
Testing a large IGT engine as a whole or testing a part or component of the engine is both very expensive and very difficult. When a large engine is tested, the power generated must be dissipated, such as by using the energy immediately or storing it for future use. One method of dissipating the energy produced is to use it to drive an electric generator. Energy produced from the electric generator can be supplied back into an electrical grid. However, engine testing might only last for a few hours. Supplying this large amount of electricity to the grid for a few hours and then stopping can cause significant problems for the power company, especially if the gas turbine engine gets tripped offline due to a problem during testing.
Another problem with testing industrial engines is that the cost to test is very high. In some IGT engine test beds, instead of using an electric generator to supply the resistance load, a water break or electrical heater resistors can be used to dissipate the load produced by the engine. These means of dissipating the load have advantages over the electrical power production described above in that a disturbance to the electrical grid is not produced. However, the disadvantage is that all of the energy produced is lost.
Testing the combustor or turbine component of a large aero or industrial engine requires a high flow rate of high-pressure air. Test times can last many hours, depending on the required warm-up time to achieve steady test conditions and the number of measurement points required for a complete data set. A typical facility is located in Cologne, Germany, operated by the German Aerospace Center (DLR). This facility provides flow rates and pressures that are limited by the size of the compressors at the facility. Therefore, large engine combustors are often tested in segments and large industrial gas turbine combustors are tested as individual cans. Full annular combustor testing for large engine or industrial gas turbines, even though desirable for combustor development, is not possible due to flow and pressure limitations at facilities such as DLR. Future component testing requires even higher flow and higher pressures, and to build a test facility with compressors large enough to supply the desired flow and pressure levels for multi-hour full annular testing would require a large capital investment, for example, as much as $400 million.
In a power plant that uses an IGT engine to drive a generator and produce electrical power, the electrical power required by the local community cycles from high loads (peak loads) to low loads such as during cool days or at night. One process to match electric supply with demand of an electrical power plant is to make use of compressed air energy storage (CAES) system. At these CAES facilities, during times of low loads, instead of shutting down an engine, the engine is used to drive a compressor instead of an electric generator to produce high pressure air that is then stored within as an underground cavern such as a man-made solution-mined salt mine cavern. The compressed air is then supplied to the combustor to be burned with a fuel and produce a hot gas stream that is passed through the turbine to drive the electric generator. This system replaces use of a compressor with use of the compressed air stored within the reservoir.
The conditions under which testing of these large engines and their components occurs should also be considered. When testing a gas turbine engine such as a large industrial engine or an aero engine or a component of one of these engines, the engine or component needs to be tested at different operating condition other than just the steady state condition. Engine partial load conditions must be tested, and such tests require different fuel and compressed air flows. Also, the loads on the engine vary during the testing process from a full load at the steady state condition to partial loads. Thus, the amount of energy dissipated varies during the engine testing process.